Deposition of aluminum



June 27, 1961 E. R. BRElNxNG ETAL 2,990,295

DEPosITIoN oF ALUMINUM Filed Nov. 7, 1958 2 sheets-sheet 1 INVENTORS. 2ML-'R IMBERT BRE/mvo nous M. Buro# BYFR/rz o. psvrscnsn rYoRNEF wrm fra/42 Juner27, 1961 E. R. BREINING ET AL 2,990,295

DEPosITIoN oF ALUMINUM Filed Nov. 7. 1958 2 Sheets-Sheet 2 da/m Afro RNE/f5 United States Patent O Wi 2,990,295 DEPOSITION OF ALUMINUM Elmer Robert Breining, Dayton, Wilbur M. Bolton, Piqua, and lFritz 0. Deutscher, Dayton, Ohio, assignors, by mesne assignments, to Union Carbide Corporation, New York, N.Y., a corporation of New York Filed INov. 7, 1958, Ser. No. 772,590

Claims. (Cl. 117-106) y This invention relates to improvements in the deposition of aluminum from heat decomposable, gaseous aluminum bearing compounds.

The invention has as primary objects the deposition of aluminum of extremely high purity and of considerable thickness with a relatively high deposition rate of the metal.

It has already been found, as described in the copending application of Elmer Robert Breining, Wilbur M. Bolton and Fritz O. Deutscher, entitled Aluminum Plating, and led of even date herewith, that the inclusion with the aluminum plating gas of an unsaturated compound, such as an olen, materially aids the aluminum deposition. It has now been found that the inclusion of an oxidizing agent with the aluminum compound increases the plating rate of aluminum from heat decomposable aluminum bearing compounds. Further, the inclusion of an agent such as oxygen gas with the aluminum bearing compound provides for more pure deposits at lower plating temperatures and deposits which are bright, ductile, adherent, uniform and of ygreater thickness.

The oxidizing agent which is most suitably intermixed with the aluminum plating gas may be oxygen or an oxygen containing compound. Suitable for mixing with the gaseous phase of the aluminum compound is nitrous oxide.

The most suitable aluminum containing compounds are the organo-aluminums and particularly the alkyl aluminums. Alkyls such as aluminum tri-isobutyl, aluminum tri-isopropyl, aluminum tri-isoamyl and mixed aluminum alkyls such as diethyl isopropyl aluminum and ethyl propyl isobutyl aluminum serve the purpose.

The oxygen content of the 4gaseous phase of the plating material should be suiciently low to prevent oxidation of deposited aluminum when the metal product is desired. It has been found that as little as 0.01 mol percent of oxygen based on the mols of the aluminum plating compound is effective to provide advantages in accordance with the invention. Somewhat more oxygen is generally useful in conjunction with the alkyl aluminum compounds, up to 0.2 mol percent having been found to be very useful and to provide completely reproducible results.

As set out hereinbefore olefins such as isobutylene 'also aid the aluminum deposition and are preferably ernployed in conjunction with the oxidizing agent in the plating atmosphere. Propylene and 3-methyl butene-l serve this purpose. The unsymmetrical or symmetrical compounds such as alpha butylene and beta butylene are effective.

In the usual practice of the invention the oxidizing agent in gaseous form is introduced with a carrier gas to the plating atmosphere, which atmosphere is in contact ywith a substrate to be plated. It has been found desirable under conditions where the substrate is relatively easily oxidized and the oxygen content is 0.2 mol percent and above, to rst effect a plating of aluminum in the absence of oxygen. This tends to avoid oxidation of the substrate and results in improved adhesion. When an initial thin coating of aluminum is attained on the substrate the oxidizing agent is then introduced as plating continues.

2,990,295? Patented June 27, 1961 The carrier gases used in the practice of the invention are suitably inert Vgases such as argon, nitrogen and helium. Further the carrier gases themselves are substantially free of oxygen prior to utilization in the process, the gases testing less than 0.0005 percent oxygen by volume.

While the exact mechanism of the action induced by the oxidizing agent is not presently known, it appears, as a theory, that the organo-aluminum compounds indecomposing give rise to the presence of free radicals which tend to some extent to occasion, by their reactivity, a carbon deposit with the aluminum metal. The presence of oxygen overcomes this. The olens tend to act in somewhat a similar way. For example, it has been found that utilizing the organo-aluminum with a carrier, such as argon, normally produced deposits having about 2 percent carbon by weight. The use of an olen, such as isobutylene, consistently resulted in deposits having 0.5 percent carbon or less. When an oxidizing agent, such as oxygen gas, is added to the plating atmosphere, only very minute traces of carbon are found, yielding an aluminum deposit of a high degree of purity, ductility, adherence and of very considerable importance a deposit which is repeatedly reproducible.

The invention will be more fully understood by reference to the following detailed description and accompanying drawings wherein:

FIGURE l is a schematic illustration of apparatus useful in the practice of the invention;

FIGURE 2, is a fragmentary and somewhat enlarged view illustrating the plating chamber of FIGURE 1; and

FIGURE 3 is a view of a copper tube plated in accordance with the practice of the invention.

lReferring to the drawings, the numeral 1 designates a tube of copper which is contained Within a tubular element 2. The copper tube 1, as shown in FIGURE l, is mechanically connected into a conduit having portions 3a, 3b, the tube being supported between the ends either by being swaged into the conduit or threaded into the conduit, or the like.

The tube 1 is heated through electrical resistance means indicated at 4, the electrical resistance being connected through leads 5 to a Variac 6, whereby the degree of heating may be controlled. 'I'he leads 7 are thermocouples connected to a control unit 9. Conduit portion 3b includes a valve 10 and terminates in a container 11 having a pool 12 of an absorbent liquid, such as heptane.

A carrier gas such as argon, which is substantially free of oxygen, is supplied to the system through owmeter 13, regulating valve 14 and hand valve 15in conduit 16. 'lhe unsaturated gas, usually an olefin, such as isobutylene, is supplied to the system through iiowmeter 17, regulator valve 1S and hand valve 19 in conduit 20. The argon and isobutylene mix at 21 and pass through heater 22 controlled by Variac 23, and conduit 24 to the vaporizer 25. A valve 26 is provided in conduit 24.

'Ihe vaporizer 25 has an electrical resistance heating element 27 regulated through Variac 28. The outlet line 29 of the vaporizer communicates with conduit 3a for the passage of plating gas to the tube 1. For the passage of a carrier gas to the tube 1 for the purpose of purging the tube, in initiating an operation, a by-pass line 30 having a valve 31 is provided.

The numeral 32 designates the source of the metal bearing compound, in this instance tri-isobutyl aluminum, a liquid. A conduit 33 communicates source 31 with a filter 34, and flowmeter 35 in conduit 36 which also has valves 37, 38. The metal bearing compound is passed under pressure as a liquid to conduit 24, where it mixes with the argon and isobutylene, and is passed on to the vaporizer." The vaporized tri-isobutyl aluminum with the argon fand isobutylene pass to the tube 1 through condzuii PQIQIla.

A source of hydrogen isv designated at 39 and cornmunicates through valve 40 with ilowmeter 41, valve 42 and heater 4,3v controlled by Variac 44. The branch conduit 46 having valve 47 provides for passage of hydrogen to the Ytube 1 when valves 31 and 48 are closed.

Oxygen containing argon is supplied to the system owmeter 49, regulating valve 50 and hand valve 51 in conduit 52. This oxygenated carrier mixes with the isobutylene at 53.

For operation at atmospheric pressure, with all valves closed except 14, 1S, 31 and 10, argon is passed through the system to expelV all air. The argon bubbles through the heptane 12 and escapes or is recovered as desired.

Withk the argon flowing, valves 40, 41 and 47 are opened and the argon ow is closed oli; energy is applied to heater 43 and hot hydrogen gas passes through tube 1 to insure of thorough de-oxidation of the interior surface of the tube. After de-oxidation the hydrogen ow is Vshut off. Then with argon again owing isobutylene, argon and the tri-isobutyl aluminum are fed to vaporizer 25. For this purpose the vaporizer is suitably at a temperature of 475 F.; the argon and isobutylene heater 22 at 320 F.; the tube 1 at 525 F., While the exhaust gases `fed to the heptane absorbent are at 225 F. The hydrogen heated When used to effect de-oxidation is Ysuitably at a temperature of at least 575 F. and may be as high as l200 F. v

ATypical iiow rates of the components making up the plating atmosphere, at 70 F. and atmospheric pressure (14.7 lbs. per square inch) as a basis, are:

`108 cc. per minute of argon 88 cc. per minute of isobutylene, and 42.7 cc. per minute of tri-isobutyl aluminum The tri-isobutyl aluminum measurement is also about 0.42 cc. per minute ofthe liquid.

The vaporized aluminum tri-isobutyl together with the oxygen-free argon and isobutylene pass to the tube 1 and aluminum deposits on the interior of the tube. The tri-isobutyl which is not decomposed is absorbed at 12 with other components of the exhaust gas. Argon bubbles through the heptane and escapes or isrecovered if so desired.

With a thin coating of aluminum on the interior of tube 1 valve 15 is closed and oxygenated argon ows through valves 50 and 51 to rnix'with the isobutylene and then the tri-isobutyl aluminum. The quantity of oxygen required in the plating atmosphere is very small. At 0.2 mol percent based on the tri-isobutyl aluminum the oxygen is entirely effective to provide bright, adherent deposits of substantially carbon free aluminum.

Particularly, it is to be noted that the introduction of the oxygen permits thick deposits-5 mils and aboveto be attained. This is in contrast to the deposition which takes place when the tri-isobutyl aluminum decomposes, as the thickness then tends to be limited.

When the oxygen content is low, 0.01 mol percent, for example, the initial deposition 'with oxygen free argon is not necessary; this initial deposition yst'epis a precaution to avoid oxidation of the copper. The plating atmosphere, employing the oxygenated argon and with valve 31 closed is passed to the tube 1 until the desired thickness of aluminum deposit is attained, as illustrated at '54 in FIGURE 3. In a time of about 2 hours, under the above conditions ou a tube having a diameter of 'SAG of an inch and a length of l0 inches, a 4.7 mil thickness over the interior is obtained.

Importantto the nature of the procedure is the reproducibility of results; repetitive tests have resulted in ductil`e,'adherent, bright deposits of superior quality. vThe highest plating rates have been attained utilizing 'ai-,gon as theV carrier; howevennnogen has been used as theffcarrier; accordingly air may be substituted for the @rassegnarsiof.assasfjasitwgsawfif:

It will be understood that this invention is susceptible to modiiication in order to adapt it to dlerent usages and conditions and accordingly, it is desired to comprehend such modifications within this invention as may fall within the scope of the appended claims.

What is claimed is: K

l. In an aluminum deposition process, wherein a substrate ,is heated in the presence of a heat decomposable organo-aluminum compound to deposit aluminum on the substrate, Vthe improvement which comprises the step of interrnixing, with Vthe gaseous phase of a heat decomposable organo-aluminum compound, arquantity of an oxidizing agent in gaseous form, said quantity of oxidizing agent being present to the extent of between about 0.01 mol percent and 0.2 mol percent based on the mols of the organo aluminum compound present.

2. In an aluminum deposition process, wherein a substrate is heated in the presence of a heat decomposable organo-aluminum compound to deposit aluminum on the substrate, the improvement which comprises the step of intermixing, with the gaseous phase of a heat decomposable organo-aluminum compound, a quantity of oxygen, said quantity of oxidizing agent being Ypresent to the extent of between about 0.01 mol percent and 0.2 mol percent based on the mols ofthe organo aluminum compound present.

3. In an aluminum deposition process, wherein a substrate isheated in the presence of a heat decomposable organo-aluminum compound to deposit aluminum on the substrate, the improvement which comprises the step of intermixing, with the gaseous phase of a heat decomposable organo-aluminum compound, a quantity of a carrier gas containing an oxidizing agent in gaseous form, said quantity of oxidizing agent being present to the extent of between about 0.01 mol percent and 0.2 mol percent based on the mols of the organo aluminum compound present.

4. In an aluminum deposition process, wherein a substrate is heated in the presence of a heat decomposable organo-aluminum compound to deposit aluminum on the substrate, the improvement which comprises the step of intermixing, with the gaseous phase of a heat decomposable organo-aluminum compound, a quantity of a carrier gas containing oxygen, said quantity of oxidizing agent being present to the extent of between about 0.01 mol percent to 0.2 mol percent based on the mols of the organo aluminum compound present.

5. In an aluminum deposition process, wherein a substrate is heated in the presence of a heat decomposable aluminum-alkyl compound to deposit aluminum on the substrate, the improvement which comprises the step of intel-mixing, with a heat decomposable aluminum alkyl in the gaseous phase, a quantity of a carrier gas containing an oxidizing agent, said quantity of oxidizing agent being present to the extent of between about 0.01 mol percent to 0.2 mol percent based on the mols of the organo aluminum compound present.

6. In an aluminum deposition process, wherein a substrate is heated in the presence of a heat decomposableV aluminum-alkyl compound to deposit aluminum on the substrate, the improvement which comprises the step of intermixing, with a heat decomposable aluminum alkyl in the gaseous phase, a quantity of a carrier gas containing oxygen, said quantity of oxidizing agent being present to the extent of between about 0.01 mol percent to 0.2 mol percent based on the mols of the organo aluminum compound present.

7. In an aluminum deposition process, wherein a substrate is heated in the presence of a heat decomposable aluminum-alkyl compound to deposit aluminum on the substrate, the improvement which comprises the step of intermixing, with a heat decomposable aluminum alkyl in the gaseous phase, a quantity of a carrier gas contain- 'ing oxygen to the extent of between about 0.01 mol percent and 0.1 mol percent of the carrier gas.

"8. In an aluminum deposition process, the steps of heating a substrate on which the aluminum is to be deposited in a substantially oxygen-free atmosphere to a temperature sucient to decompose a gaseous aluminum alkyl, and thereafter contacting the heated substrate with a gas ow containing a heat decomposable aluminum alkyl and an oxidizing agent in an amount which is insufficient to substantially oxidize deposited aluminum to occasion deposition on the substrate of a substantial thickness of substantially pure aluminum, said amount of oxidizing agent being present to the extent of between about 0.01 mol percent and 0.2 mol percent based on the mols of the aluminum alkyl present, and thereafter removing the substrate from the gas ow.

9. In an aluminum deposition process, the steps of heating, in a substantially oxygen-free atmosphere, a metallic oxidizable substrate having a surface substantially free of oxide and on which aluminum is to be deposited, to a temperature sucient to decompose a gaseous aluminum alkyl, contacting the so-heated substrate with a gas ow containing a heat decomposable aluminum alkyl and a carrier gas to eiect deposition of aluminum on the substrate, continuing the gas llow to build up the aluminum thickness on the substrate, then flowing with the aluminum alkyl a carrier gas containing an oxidizing agent in an amount which is insucient to substantially oxidize deposited aluminum and to further increase the deposition of the aluminum, said amount of oxidizing agent being present to the extent of between about 0.01 mol percent and 0.2 mol percent based on the mols of the aluminum alkyl present, and thereafter removing the substrate with the aluminum thereon from the gas ow.

10. In an aluminum deposition process, the steps of heating, in a substantially oxygen-free atmosphere, a metallic oxidizable substrate having a surface substantially free of oxide and on which aluminum is to be deposited, to a temperature sucient to decompose a gaseous aluminum alkyl, contacting the so-heated substrate with a gas flow containing a heat decomposable aluminum alkyl, an olefin and a carrier gas to eiect deposition of aluminum on the substrate, continuing the gas flow to build up the aluminum thickness on the substrate, then flowing with the aluminum alkyl, the olen and carrier gas an oxidizing agent in an amount to further increase the deposition of aluminum without causing any substantial oxidation of the aluminum, said amount of oxidizing agent being present to the extent of between about 0.01 mol percent and 0.2 mol percent based on the mols of the aluminum alkyl present,v and thereafter removing the substrate with the aluminum thereon from the gas flow.

References Cited in the le of this patent UNITED STATES PATENTS 2,876,137 Drummond Mar. 3, 1959 2,919,207 Scholzel Dec. 29, 1959 FOREIGN PATENTS 765,480 Great Britain Ian. 9, 1957 OTHER REFERENCES Powell et al.: Vapor Plating (1955), John Wiley & Sons, Inc., NeW York. (Copy in Scientic Library and in Div. 25 (pp. 137 and 140). 

1. IN AN ALUMINUM DEPOSITION PROCESS, WHEREIN A SUBSTRATE IS HEATED IN THE PRESENCE OF A HEAT DECOMPOSABLE ORGANO-ALUMINUM COMPOUND TO DEPOSIT ALUMINUM ON THE SUBSTRATE, THE IMPROVEMENT WHICH COMPRISES THE STEP OF INTERMIXING, WITH THE GASEOUS PHASE OF A HEAT DECOMPOS- 